For a long time it was believed that the infrared absorbtion spectrum of water "vapor" could be explained by interatomic vibrations or by modes of individual water molecules, hereinafter referred to as "monomers". Recently it has been determined that this absorption phenomenon cannot be adequately explained by monomers but rather was due to molecular aggregates or "clusters"of wter molecules in a vapor phase.
It has been known that substances which absorb infrared radiation also emit radiation. The infrared emission spectra of water vapor, and especially that of steam, as reported by the present applicant in Infrared Physics 19, 49 (1979), in an article entitled "Variations in Emission Spectra from Warm Water Fogs", show features which indicate that water cluster species are present. These spectra may be measured by infrared radiometers.
Infrared systems are used in a wide variety of applications today. Such systems are used in missile guidance, surveillance, thermal imaging, and night vision apparatus. In addition there has been interest shown in the use of aerosols and smokes in infrared and electronic countermeasure applications.
In the applicant's infrared radiometric measurements of saturated steam, reported in the article above, intense spectral activity was observed which gave evidence of large water cluster populations. This article indicated that a direct proportionality exists between ion populations in water vapor or moist air and infrared spectral activity. The aforementioned tests also indicated that it would be possible to measure electrical conductivity due to ions in water vapor. These ions would have similar dependencies upon vapor pressure and temperature as the infrared spectral activity had.
The problem with prior art devices which used standard test instrument for measuring electrical conductivity of moist air was that frequently there were errors due to leakage across the insulators of the measuring device. Prior art devices, like the Gerdien tube, which utilized tubes or channels frequently had very poor ratios of electrode area to electrode spacing. Thus the prior art devices used for measuring electrical conductivity in moist air were insensitive, subject to errors, and often required very specialized test equipment in order to perform satisfactorily in a moist environment.